Perlite is not a trade name but a generic term for naturally
occurring siliceous volcanic rock. The distinguishing feature which sets perlite apart
from other volcanic glasses is that when heated to a suitable point in its softening
range, it expands from four to twenty times its original volume.

This expansion process is due to the presence of two to six
percent combined water in the crude perlite rock. When quickly heated to above 1600 F (870
C) the crude rock pops in a manner similar to popcorn as the combined water vaporizes and
creates countless tiny bubbles in the softened glassy particles. It is these tiny
glass-sealed bubbles which account for the amazing lightweight and other exceptional
physical properties of expanded perlite.

The expansion process also creates one of perlite's most
distinguishing characteristics: its white color. While the crude perlite rock may range
from transparent to light gray to glossy black, the color of expanded perlite ranges from
snowy white to grayish white.

Expanded perlite can be manufactured to weigh from 2 lbs/ft3
(32 kg/m3) to 15 lb/ft3 (240 kg/m3) making it adaptable
for numerous uses, including filtration, horticultural applications, insulation, inert
carriers and a multitude of filler applications.